In the cartridge of the von Behren patent, magnetic recording tape is driven by a thin, continuous, elastic, flexible, pretensioned belt which in turn is driven by a single reversible drive motor that provides rapid acceleration and deceleration of the recording tape in either direction. In such a cartridge, pressure is exerted by the belt on the tape pack over an extended area, and the pressure arises solely from the tension in the belt. When the cartridge shown in FIG. 1 of the von Behren patent was first marketed in 1972, its recording tape had a width of 1/4 inch (0.64 cm), a thickness of one mil (0.025 mm), and was driven at 30 inches (76 cm) per second. Data were originally recorded on the tape at a density of 1600 flux reversals per inch (630 per cm). The recording tapes of current cartridges may be as thin as 0.6 mil (0.015 mm) and may be driven at 90 or more inches (229 cm) per second, and data may be recorded at densities of about 10,000 flux reversals per inch (3900 per cm). At these higher tape speeds and recording densities, intimate tape-to-head contact and uniformity of tape speed have become more critical to avoid data handling errors. Intimate tape-to-head contact requires uniform tape tension, and a failure to achieve uniform tape tension is evidenced by belt slippage and variations in tape speed. Even though no problem was encountered due to variations in tape tension when the cartridge was first introduced, the higher tape speeds and recording densities have created a need for better control of tape tension in order to maintain data signal reliability.
The belts of current versions of the von Behren cartridge are made from polyurethane film having a thickness of about 5 mils (0.25 mm). For a cartridge whose hubs are on axes about 2.4 inches (6 cm) apart, the belt may be made by stamping out a ring having an outside diameter of about 1.8 inches (4.6 cm) and an inside diameter of about 1.2 inches (3.2 cm). Using rotating shafts, the ring is stretched and distorted into a cylindrical belt which is positioned around the tape pack of the cartridge. When so positioned, its length is about 15 inches (38 cm) and its width is about 1/8 inch (0.3 cm).
Recording tape packs which are driven by pretensioned elastic belts are also shown in U.S. Pat. Nos. 3,305,186 (Burdorf), 3,544,038 (Smith), 3,514,049 (Decker), and French Pat. No. 1,297,446 (Willis). Another such tape pack is interdyne's Model IU 1650.